In general, in order to supply a pressurized oil from a hydraulic source including a hydraulic pump to a hydraulic actuator (a hydraulic motor, a hydraulic cylinder, for example), a construction machine represented by a hydraulic excavator is configured to be provided with a multiple valve device composed of a plurality of spool valves (directional control valves) between the hydraulic actuator and the hydraulic source.
This type of conventional-art multiple valve device includes a valve housing provided with oil passages on a hydraulic source side having a plurality of spool sliding bores and communicating with each of the spool sliding bores and an actuator side and a plurality of spools provided by being inserted in each of the spool sliding bores of the valve housing and selectively communicating with/shutting off the oil passage on the hydraulic source side and the oil passage on the actuator side.
As the valve housing used in such a multiple valve device, three types, that is, a stack type in which three or more housing blocks are made to abut against and to overlap each other on the joining surfaces thereof, a two-split type in which two housing blocks formed by being split into two parts abut against each other at the position of the joining surface, and a mono-block type in which the entirety is formed as a single housing block are known, for example (Patent Documents 1, 2, 3, and 4).